Process and apparatus for cracking oils



Dec. l5, 1931. E. T. EARNEST 1,836,910

PROCESS AND APPARATUS FOR CRACKING OILS Filed May 5l, 1928 @YQ/VZW lfm PUMP

Patented Dec. 15, 1931 UNITED STATES PATENT OFFICE ELISEA T. EABNET, OF PORT ARTHUR, TRAS, ASSIGNOB. TO THE TEXAS COMPAN Y,

OF NEW YORK, N. Y., A CORPORATION OF DELAWARE PROCESS AND APPARATUS FOB. CRAC'KING OILS Application led Iay 81,

The invention relates primarily to a method of converting higher boiling hydrocarbon oils into lower boiling oils and to suitable apparatus for carrying out the novel features of the improved method. More particularly, the invention has to do with the 4provision of more uniform operating conditions for various portions of a cracking system, or the like, to the end that a greater uniformit in the products of the system will result. or this purpose it is contemplated providing auto` matic means for effecting the desired control over those phases of the system which most vitally affect the products created in the course of operation. A feature of the invention in its specific embodiment, as herein disclosed, involves the provision of automatic pressure-regulating means to control the pressures maintained within the dephlegmafor or separating tower which is associated with a tar stripping unit forming a part of a complete cracking system.

In the operation of some cracking processes in which oil is converted into the lighter constituents through the application of heat and pressure in any of a variety of ways, it is the practice to draw off the residual oil' lfrom the main cracking system from time to time and to strip it while hot by relieving the pressure on this oil so as to permit a large portion of it to be converted directly into vapors. Normally, in systems of this character, the withdrawal of the residues or tar bottoms from the main cracking units must take place at periodic intervals in order to prevent the clogging up of the tar drawing lines, which would result from a continuous withdrawal of this material in a relatively fine stream. This brings about an undesirable condition in the system, since it results in the placing of a variable load, particularly upon the tar stripping unit. Thus, at a time when a charge of residual oil is being passed from a portion ofV the main cracking system into some section such as the expansion chamber of the stripper, the pressure in the latter will rise to a considerable degree. After the tar drawing valves are closed, this pressure will gradually drop until just before the introduction of a 1928. Serial No. 281,650.

new charge into the expansion chamber, when a minimum pressure will be present.

,It will be apparent that .this continual variation of the pressure in the tar stripper brings about a very irregular operation of the related portions of the system and prevents any. degree of accuracy in the fractionation of the vapors which are released in the expansion chamber. Furthermore, where it has been customary in the past to pass the residual material from the first expansion chamber into another vessel or distillation zone, such as a steam still for further stripping of the tar, considerable rregularit in the operation of the latter has resulted. fue to this irregularity in the operation of the System, the overhead products of the dephlegmator, or other fractionator, associated with the first expansionchamber are of too variable composition to be used directly and the overheadproducts from the second chamber, or steam distillation zone, have been of too irregular composition to b e returned to the original cracking system as recycle stock. A primary object of the present invention, therefore, has been to correct these difiiculties in the operation of the tar stripper and to produce not only a uniform final product but also a uniform recycle stock.` Other objects and advantages will become apparent from so the detailed description which will now be given in conjunction with the accompanying drawing in which the single figureillustrates diagrammatically one suitable form of apparatus for carrying out the invention.

Referring now to the drawing, a ump 10 may bc provided for the purpose of fieeding a fresh charge. of oil of any suitable gravity to a crackmg'system of any suitable form, in which the oil will be subjected to a cracking temperature under a su eratmospheric ressure. For example, the cliarge may first forced through a heating coil 11 situated in a furnace (not shown) and adapted to raise the temperature of the oil above the cracking point, say, between 750 and 900 F. under a pressure of from 100 to 500 pounds or more, if desired. The heated oil may then be passed through a transfer line 12 into one or more of a series of interconnected 100 drums or stills 13. These may be merely heatinsulated or may'be supplied with a small amount of external heat by means not shown, and are preferably connected by a pipe 14'below the liquid level and a pipe 15 above the liquid level so that both the liquid body of oil and the vapors will pass freely from one to the other. VYhile two stills are disclosed in the drawing, it will be understood that a single drum might be provided, or any greater number might be employed, if desired.

Vapors generated in these stills may be led by a suitable vapor line 16 to a dephlegmator or fractionating tower 17, which may be in the form` of a bubble tower, where a separation between the lighter and heavier constituents may be effected. The lighter constituents will pass out at the top of the tower into a. reflux condenser 18 and-on to a final condenser 19 and collection receptacle 20. It will be understood that a portion of the-vapors may be returned from the condenser 18 and used as a temperature regulating medium for the tower. Condensate which collects in the base of the tower may be led through aline 21 to a pump 22 which is adapted to return this backtrapped material to the heating coil 11, either at the top of the latter where the fresh charge is introduced, or at an intermediate point 221.

The foregoing portions of the system may be operated under a substantially uniform pressure throughout, or, if desired, a drop in pressure may be brought about between the coil 11 and the stills 13, or between the latter and the tower 17, or even at both points.

From time to time the residue which collects in the lower portions of the stills 13 may be withdrawn and passed through a line 23 into an expansion chamber 24 forming the first element of a tar stripping unit. In the chamber 24 the pressure will be materially reduced so that a large portion ofthe residue entering the latter' will be immediately vaporized, due to its own contained heat. Vapors th'us formed may be passed by the vapor line 25 through a valve 26 and into any suitable form of dephlegmator or fractionating tower 27. A portion of the vapors will be condensed in the tower but those which remain in vapor form may pass beyond through a reflux condenser 28 and a final condenser 29 into a storage receptacle 30.

Now, as previously explained, the pressure within the chamber 24 will fluctuate to a considerable extent between a maximum, created at the time the residue is being passed into the chamber, and a minimum, which will exist just prior to the passage of the next batch of residue into the chamber. This variation in pressure may, for example, cover a range between a minimum of 5 pounds and a maximum of 50 pounds, and even greater variations may occur at times.

In order that these variations in pressure may not be passed along to the fractinating tower 27 and thus interfere with the proper separation of the different components therein, it is proposed by the present invent-ion to regulate the opening of the valve 26 in accordance with the pressure which exists in the tower. For this purpose a pressure regulator 31 is provided and arranged so that a diaphragm within the latter will control the. extent of the opening of the valve.` Operation of the diaphragm will be controlled by the pressure withinl the fractionating tower through connections comprisin a line 32, a trap 33, and another line 34, ]oining the main vapor line 25 at a point beyond the valve 26. This construction may be such that when the pressure within the tower 27 reaches a maximum of, say, 5 pounds, the regulator 31.will substantially close the valve 26. As the pressure within the tower tends to drop below thisamount, the valve 26 may be gradually opened, thus tending to maintain a uniform pressure within the tower.

At times it may be found that an attempt to hold the pressure within the tower below a maximum of, say, 5 pounds will give rise to the development of an excessive pressure within the expansion chamber 24. To avoid any difficult-ies which might varise from this source, a by-pass line 35 leading from the vapor line 25 may be provided and this line may be equipped with a pressure lreliefvalve 36 which may be set to blow off at any desired pressure, as, for example, 50 pounds. When the relief valve is operated upon the buildin up of this maximum pressure within the c amber 24, the vapors will be passed through a line 37 which rejoins the line 25 beyond the pressure-regulated valve 26. However, in order thatl the control of the tower may not be completely destroyed by such sudden increases in pressure, the by-pass line 35-37 is provided with a separate pressure-regulated valve 38. This valve may be controlled by a pressure regulator 39 connected by means of a line 40, trap 41 and line 42 to the line 37, which is in open communication with the tower. This arrangement may be such that a ressure up to 10 pounds, for example, may e permitted within the tower whenever the relief valve has been opened. Thus, when the pressure within thei tower reaches the maximum of 10 pounds, even the valve 38 may be closed so that no additional vapor will be introduced and the pressure within the chamber 24 and in the lines 25 and 35 will be permitted to tempo- `rarily build u but as soon as the pressure in the tower rops below this maximum of ten pounds, the valve 38 may be opened slightly to permit the passage of additional vapors. It will be understood, however, that the by-pass line does not come into play until the pressure within the expansion chamber has exceeded the maximum deter- (itl mined by the relief valve 36, and it remains active only so long as this pressure is exceeded.

Condensate which has collected at the base of the fractionat-ing tower may be passed by means of a line 43 to a pump 44 which may then return this recycle stock to the heating coil 11 at either of the points mentioned with respect to the backtrap from the tower 17. It may be found desirable to control the fiow ofthe condensatefrom the tower 27 by means of a. valve- 15, which is adapted to be operated by a fioat 46 within the tower.

The residue which is collected within the expansion chamber and is not vaporized under the reduced pressure inayif desired, be passed to suitable storage, although it is deemed preferable to subject this residue to further stripping-actioi'i. For this purpose, a` pipe 47 may be provided to" lead the residue --into a' line 48 and through a valve 49 into a second chamber, which may be in the form of astem still50. Now, in order to maintain uniform pressure 'conditions as nearly as possible Withiri the steam still, the valve 49 may be controlled by a suitable pressure-reguhating device 51.4 This may be connected by a line 52 through a trap 53 to a point in the line 48 beyond the valve 49. `It will be. apparent that by virtue of the connections iud'icated, the opening of the valve 49 will depend upon the pressure conditions within the steam' Still. The Withdrawai of the residual material fromV `the chamber 24 will preferably be controlled, also, by means of a 'salve 54 Lwho"se operation may be directly mntrlled' in any suitable way from a. oat 55.

At times nav found that the maxi- :nur pressure the steam stillv means of the regulator 51 will result. inf thfe closing of the valve 49 to such an extent thatuthe level within the chamber will'l rise to an undesirable degrec. To o ii'set contingency such as this.r

a second; loat56'is provided within this chamber t a' height* above which it is not desired" to: have themateria'l' rise. lVh'en this point is reached @valve 57 will be opened under control oi float and will permit mssag' ofthe residue into a by-pass line 58,v which then serve topass the material around' the pressure-regulated valve 49 and lirectly into the steam still 50.

Any additionalI vapors vwhich may be genei-ated in the steam still may be lcd through a vapor line 59 to any suitable condensing and collecting apparatus, if desired; or, after passing througfhfa' condenser 59a, they may be passed by means of a' pump 60 into the heating coil 11, together with the recycle. stock taken' from the base ofthe tower 27. The final' residue which remains in the still 50 may vbe drawn off through a line 61 and sent to any suitable form of storage. If deslred, this line may be provided with a valve 62 controlled by a fioat 63 within the steam still.

By maintaining substantially constant operating conditions in the tower 27 and the still 50, the products collected beyond these elements -may be regulated to any desired and uniform constituency. Thus, the product collected in the receptacle30 may be suitable for blending with the condensate in the collector 20 to form a finished gasoline, without the necessity of re-running either component. Similarly, the condensates from the tower 27, as well as the vaporized portions taken from the still 50, will be found to be satisfactory for recycling through the same cracking system.

While the tar stripping unit has been disclosed herein as related to a single cracking system or battery of stills, it will be understood that the automatic control features are just as applicable to a' system in which a common tar stri vper is employed in connection witha num er of separate cracking systems orbatteries of stills.

One specific form of apparatus adapted to carry out the features o the present invention has been described in detail herein, but it will be understood that this is merely for the purpose of illustration and that the invention is capable of many variations. It is not desired to be limited in the scope of the invention other than by the claims which follow.

What I claim is:

1. In a process for converting higher boil- 100 ing oils into lower boiling oils by the application of heat and pressure the steps comprising passing the residue intermittently from the conversion zione into a' zone of reduced pressure wherein a wide variation in 105 pressure is encountered, passing the vapors released upon the reduction of pressure into a dephle'gmator to eifecta separation between the' lighter and heavier constituentsof the vapors, and maintaining a substantially con- 110 stant ressure withinthe dephlegxnator.

2. n' a process for convertin higher boilingoils into lower boiling oilsiby the applicationl ofheat and pressure the steps comprising passing the residue intermittently from 115 the conversion zone in to a zone of reduced pressure wherein al wide variationv in pressure is encountered, passing the vapors released upon the reduction of pressure into a dephlegmator to effect a separation between 120 the lighter and Aheavier constituents of the vapors, and maintaining a substantially constant pressure within the dephl'egmat'or below the minimum pressure within the zone of reduced pressure.

3. In a process for converting higher boiling oils into lower` boiling oils by the application of heat and pressure the steps comprising passing the residue intermittently from the conversion zone into a zone of re- 130 duced pressure wherein a wide variation in pressure is encountered, passing the vapors released upon the reduction of pressure into a dephlegmator to effect a separation between 5 the lighter and heavier constituents of the vapors, maintaining a substantially constant pressure within the dephlegmator below the minimum pressure within the zone of reduced pressure until a predetermined maximum within the latter is exceeded, and maintaining a substantially uniform pressure within the dephlegmator higher than said minimum pressure so long as the maximum is exceeded. 4. In apparatus of the class described, means for distilling oil under pressure, an

expansion chamber, means for passing residue intermittently from said distilling means to said expansion chamber, said chamber being under a widel variable pressure, a dephlegmator, a con uit for passing vapors released in said chamber to said dephlegmator, means for regulating the flow through said conduit and adapted to maintain a uniform pressure in said dephlegmator when the pressure in said chamber remains below a predetermined maximum, and means adapted to maintain a higher uniform pressure in said dephlegmator when the pressure in said chamber exceeds said predetermined maximum.

`In witness whereof I have hereunto set my hand this 21st da of May, 1928.

LISHA T. EARNEST. 

